1. Field of The Invention
The present invention relates to television receivers and to circuitry for supplying power to the various circuits in the television receiver.
2. Description of The Related Art
A television receiver typically has three types of power supplies. As shown in FIG. 1, a main power supply receives a rectified AC line voltage (130V to 185V) and provides a relatively high regulated voltage (130 Volts) with high currents (1 Amp.) to the main loads. One of the loads on the main power supply is a secondary power supply that generates high voltage (30 KV) for the picture display tube and a variety of secondary voltages (5V, 12V, 24V, etc.) for energizing various of the circuits within the television receiver. The third power supply is the "stand-by" power supply which supplies power to the television receiver's microprocessor (and in some cases to the horizontal oscillator) both when the television receiver is "ON", and when it is "OFF". The input voltage to the stand-by power supply is usually the rectified AC line voltage and the output voltage is typically 5 Vdc to 12 Vdc. This high input voltage and low output voltage requires either a switched mode power supply or a very low efficiency series pass regulator.
A typical switched mode power supply (shown in FIG. 2) can provide large amounts of power but is relatively complex and costly even at very low power outputs. Conversely, a typical series pass regulator (shown in FIG. 3) is very low cost but is very inefficient (typically 4%). The waste power (5-10 Watts) is usually dissipated in large resistors in series with the pass element. These resistors take up space, heat other parts (whether the television receiver is "ON" or "OFF") and limit the power available from the stand-by power supply.